This invention relates to blast tube insulators for tactical rocket motor blast tubes and improved processes for making these insulators. This invention, more particularly, relates to such insulators that are rigid bodies and comprise cured phenolic resin in which certain organic and inorganic particles are intimately dispersed. This invention, still more particularly, relates to insulators such as these that exhibit char rates comparable to current phenolic insulators containing silica or carbon cloth but which are lower in density and cost.